Better unicode handling

[waf]

Character navigation / rendering / clipboard fixes for unicode characters.

Drops the wcwidth implementation and use https://github.com/spectreconsole/wcwidth (source-only package) instead.

This fixes a whole host of issues around emojis + zero-width-joiners

[codecov]

Codecov Report

❌ Patch coverage is 84.54545% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.7%. Comparing base (cc3f42a) to head (3cda2a3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/PrettyPrompt/Documents/Grapheme.cs	80.0%	2 Missing and 4 partials ⚠️
src/PrettyPrompt/Rendering/Screen.cs	53.8%	3 Missing and 3 partials ⚠️
src/PrettyPrompt/Rendering/UnicodeWidth.cs	80.0%	1 Missing and 4 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #282     +/-   ##
=======================================
- Coverage   85.0%   84.7%   -0.4%     
=======================================
  Files         46      47      +1     
  Lines       3943    3908     -35     
  Branches     603     612      +9     
=======================================
- Hits        3353    3311     -42     
- Misses       448     452      +4     
- Partials     142     145      +3     

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